According to Vastu the orientation of the house or building gives positive or negative results after 21 months or 7years or 15 years of its construction. According to classical feng-shui the main energy of a place changes after every 20 years. Thus the energy has a definite pattern of working and has definite result accordingly.
  Vastu Purush (Vastu Man)
 

Vastu purush is a concept of Indian vastu shastra which is very very  powerful and appealing too. According to  Matysa Puran,   ( sacred scriptures of Hinduism ) when Lord Shiva was fighting a war with asuras, a weird personality was created  from a drop of his sweat. He was cruel, horrifying and devoured everything on his way. Terrified Deities went to Lord Shiva and prayed for protection. Lord Shiva pressed the weird man under his foot till the war was over.
The weird man surrendered himself to Lord Shiva and begged for his forgiveness. Lord Shiva named him as Vastu Purush and ordered him that he would go on the Earth and give Health, Wealth and Happiness to the people residing there. He blessed him that the occupants there will always worship him.

Then 45 Deities including Lord Bramha collectively caught hold of Vastu Purush and threw him on the Earth with the face downwards , head in the North East and his feet in the south west. Each  body part of the Vastu Purush was given the name of the Deity who touched it. E.g. Lord Bramha touched the navel of the Vastu Purush so it was given the name of Bramha. So the centre of the house where Vastu Purusha’s navel comes is called as "Bramhasthan".

The whole idea of classical Vastu shastra is based on the Vastu Purush. I follow this system which gives me very accurate diagnosis of the problems in that place and therefore I can exactly tell the occupant about the happenings in the house. So the cure of the house is very satisfying.